21601681 has 8 divisors (see below), whose sum is σ = 21977600. Its totient is φ = 21228480.

The previous prime is 21601667. The next prime is 21601691. The reversal of 21601681 is 18610612.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21601681 - 2¹³ = 21593489 is a prime.

It is a super-2 number, since 2×21601681² = 933265244051522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21601631) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 20905 + ... + 21913.

It is an arithmetic number, because the mean of its divisors is an integer number (2747200).

Almost surely, 2^21601681 is an apocalyptic number.

It is an amenable number.

21601681 is a deficient number, since it is larger than the sum of its proper divisors (375919).

21601681 is a wasteful number, since it uses less digits than its factorization.

21601681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1359.

The product of its (nonzero) digits is 576, while the sum is 25.

The square root of 21601681 is about 4647.7608587362. The cubic root of 21601681 is about 278.5025543764.

The spelling of 21601681 in words is "twenty-one million, six hundred one thousand, six hundred eighty-one".